1. Field
The present disclosure relates to methods of high speed switching a liquid crystal, and more particularly, to methods of switching a guest-host dual frequency liquid crystal by using a back flow.
2. Description of the Related Art
Optical shutters, three-dimensional (3D) glasses for 3D cinemas, and shutters for recording 3D images perform ON/OFF switching for all incident visible light or a portion of the incident visible light. The switching may be fast and may have high transmissivity and high contrast while being independent from polarization of the incident visible light.
Most optical shutters are based on a liquid crystal (LC) technology and include a polarizer. Due to the polarizer, the optical transmittance of the shutter may be limited to 50%.
A dielectric characteristic of an LC becomes anisotropic when a low frequency voltage is applied thereto. The anisotropy may be expressed as a difference between an electric permittivity along an axis of the LC and an electric permittivity of a direction perpendicular to the axis of the LC. A representative value indicating the anisotropy may be positive or negative in a wide frequency range (from Hz to MHz).
Also, a dual-frequency liquid crystal (DFLC) shows a positive dielectric anisotropy at a voltage with a frequency lower than a transition frequency (fc) (for example, 10 KHz). The DFLC shows a negative dielectric anisotropy at a voltage with a frequency higher than the fc.
Due to the above characteristics, a horizontal state LC may be rapidly switched to a vertical state LC by applying thereto a low frequency voltage (<10 KHz), and a vertical state LC may be rapidly switched to a horizontal state LC by applying thereto a high frequency voltage (>10 KHz).
Switching of an LC induces a flow around the LC. The velocity of the flow is very small. Accordingly, the switching of the LC may not be affected by the flow. However, in some cases, the switching of the LC may be slightly accelerated by the flow. The flow at this time is referred to as a forward flow.
On the other hand, the switching may be slightly slower due to the flow. The flow at this time is referred to as a back flow or a reverse flow.